CO2 reforming catalyst, method of preparing the same, and method of reforming CO2

ABSTRACT

A CO 2  reforming catalyst may include at least one catalyst metal supported in a porous carrier. The at least one catalyst metal may include a transition metal (e.g., Ni, Co, Cr, Mn, Mo, Ag, Cu, Zn, and/or Pd). Each particle of the at least one catalyst metal may be bound with the porous carrier in a form of an alloy. The porous carrier may form a rod-shaped protruding portion around the catalyst metal particle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 35 U.S.C. §121 of U.S.application Ser. No. 13/951,634, filed Jul. 26, 2013, now U.S. Pat. No.9,084,986, issued Jul. 21, 2015, which claims priority under 35 U.S.C.§119 to Korean Patent Application No. 10-2012-0082013, filed in theKorean Intellectual Property Office on Jul. 26, 2012, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND

1. Field

The present disclosure relates to CO₂ reforming catalysts, methods ofpreparing the same, and methods of reforming CO₂ using the same.

2. Description of the Related Art

Decreasing the generation of carbon dioxide, the leading greenhouse gas,has become a globally important matter. In addition to the demand for aCO₂ decrease due to CO₂ discharge regulations, studies on converting CO₂to a specific chemical material to create added value are progressing.Since a method of converting CO₂ into H₂ and CO (which are used asprecursors of chemical materials) using a relatively high temperaturedry catalyst reaction of CO₂ and CH₄ may mitigate CO₂ accumulation andrecycle CO₂ as a useful chemical material, it has been steadily studiedin chemical factories and oil refineries where a relatively large amountof CO₂ is generated.

However, in the case of a catalyst used in converting CO₂, the catalystmay become degraded by the sintering of the catalyst particles during arelatively high temperature reaction, wherein carbon is deposited on thesurfaces of the catalyst particles.

SUMMARY

Some example embodiments relate to a relatively thermally stable andinexpensive CO₂ reforming catalyst which compensates coking depositionduring a CO₂ reforming reaction to reduce degradation and that has adesirable level of activity.

Some example embodiments relate to a method of preparing a relativelythermally stable and inexpensive CO₂ reforming catalyst whichcompensates the coking deposition during the CO₂ reforming reaction toreduce the degradation and has a desirable level of activity.

Some example embodiments relate to a method of reforming CO₂ by using arelatively thermally stable and inexpensive CO₂ reforming catalyst whichcompensates the coking deposition during the CO₂ reforming reaction toreduce the degradation and has a desirable level of activity.

According to one example embodiment, a CO₂ reforming catalyst mayinclude a porous carrier including a framework and protruding portionsdefining a plurality of pores therein. At least one catalyst metalparticle may be disposed within the plurality of pores of the porouscarrier. The at least one catalyst metal particle may include atransition metal. The transition metal may be a Group 6-12 element. TheGroup 6-12 element may be selected from the group consisting of Ni, Co,Cr, Mn, Mo, Ag, Cu, Zn, and Pd. The at least one catalyst metal particleis chemically bound to the porous carrier (e.g., in a form of an alloy).In a non-limiting embodiment, the catalyst metal particle has a halfcircular or half oval-shaped cross-sectional surface when linearly cutin a direction perpendicular to the binding surface of the catalystmetal particle and the porous carrier. The at least one catalyst metalparticle may also have a deformed surface that conforms to a receivingsurface of the porous carrier. Furthermore, the porous carrier mayinclude a protruding portion extended in a rod, needle, or sheet shapearound the catalyst metal particle.

The porous carrier may be an oxide. For instance, the oxide may be atleast one selected from the group consisting of alumina, titania, ceria,and silica oxide.

The CO₂ reforming catalyst may be participated in a CO₂ reformingreaction represented by the following Reaction Scheme 5.3CH₄+CO₂+2H₂O→4CO+8H₂  [Reaction Scheme 5]

After using the CO₂ reforming catalyst as a catalyst in the CO₂reforming reaction represented by Reaction Scheme 5 at about 700 toabout 900° C., for example, at about 850° C., for about 10 to about 200hours, the particle diameter change of the catalyst metal particle inrandom directions may have a growth rate of about 5 to about 10%compared to before using the catalyst.

In the CO₂ reforming catalyst, the longest diameter of catalyst metalparticles before being used for the CO₂ reforming reaction may have anaverage ranging from about 2 to about 20 nm.

The CO₂ reforming reaction may be performed while including water.

The porous carrier may have a specific surface area of about 20 to about500 m²/g.

The catalyst metal may have a supported concentration of about 1 toabout 15 wt %.

According to another embodiment, a method of preparing a CO₂ reformingcatalyst may include the following steps:

immersing a porous carrier in a precursor solution of at least onecatalyst metal (e.g., selected from the group consisting of Ni, Co, Cr,Mn, Mo, Ag, Cu, Zn, and Pd) and drying the same to provide acatalyst-carrier complex in which the catalyst metal particles aresupported in the porous carrier;

firing the catalyst-carrier complex at a temperature of less than orequal to about 900° C. under presence of nitrogen (N₂) or hydrogen (H₂)gas;

purging the fired catalyst-carrier complex with inert gas and reducingthe same;

immersing the reduced catalyst-carrier complex in water; and reducingthe catalyst-carrier complex.

The CO₂ reforming catalyst prepared according to the method has a halfcircular or half oval shaped cross-sectional surface when linearly cutin a direction perpendicular to the binding surface of the catalystmetal particle and the porous carrier as each catalyst metal particlebinds to the porous carrier in a form of an alloy, and wherein theporous carrier includes a protruding portion extended in a rod, needle,or sheet shape around the catalyst metal particle.

According to another embodiment, a CO₂ reforming method convertingreactants of methane, CO₂, and water into CO and H₂ according to thereaction represented by the following Reaction Scheme 5 is provided thatincludes using a CO₂ reforming catalyst in which at least one catalystmetal selected from the group consisting of Ni, Co, Cr, Mn, Mo, Ag, Cu,Zn, and Pd is supported in a porous carrier, wherein the catalyst metalparticle has a half circular or half oval-shaped cross-sectional surfacewhen linearly cut in a direction perpendicular to the binding surface ofthe catalyst metal particle and the porous carrier by binding eachcatalyst metal particle to the porous carrier in a form of an alloy, andwherein the porous carrier includes a protruding portion extended in arod, needle, or sheet shape around the catalyst metal particle.3CH₄+CO₂+2H₂O→4CO+8H₂  [Reaction Scheme 5]

The CO₂ reforming method using the CO₂ reforming catalyst is a wet CO₂reforming reaction that includes water in addition to raw materials forreforming CO₂ such as CO₂ and CH₄.

The CO₂ wet reforming reaction represented by Reaction Scheme 5 mayinclude a method of producing graphene on the surface of the catalystmetal particle of the CO₂ reforming catalyst as a side product as wellas products of CO and H₂. Graphene may be formed in 1-5 layers on thesurface of the catalyst metal particle. The reaction for producinggraphene from the reactants of CH₄ and CO₂ may be represented by thefollowing Reaction Scheme 6 and Reaction Scheme 7.CH₄

2H₂+C  [Reaction Scheme 6]2CO

CO₂+C  [Reaction Scheme 7]

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the cross-sectional surface where aNi particle is supported in alumina in a form of an alloy in the CO₂reforming catalyst including a catalyst metal of Ni and a porous carrierof alumina.

FIG. 2 is a schematic view showing the cross-sectional surface where aNi particle is supported in alumina in the nickel-alumina (NiAl)catalyst prepared according to a conventional wet process.

FIG. 3 is a schematic view showing an efficiency difference of a CO₂reforming reaction depending upon the binding shape between acatalyst/carrier in a NiAl catalyst prepared according to a conventionalwet process (left) and a NiAl catalyst prepared according to one exampleembodiment of the present disclosure (right).

FIGS. 4A-4B show SEM (scanning electron microscope) and TEM(transmission electron microscope) photographs of the catalyst accordingto Example 1.

FIGS. 5A-5B show SEM and TEM photographs enlarging a part of a Niparticle and an alumina rod in a different magnification from thecatalyst photographs shown in FIGS. 4A-4B.

FIGS. 6A-6B show graphs of measuring components of the catalyst particleportion and the rod-shaped protruding portion by EDAX in the catalystaccording to Example 1.

FIGS. 7A-7B show SEM and TEM photographs of the surface of the NiAlcatalyst prepared by a conventional wet method.

FIGS. 8A-8B show SEM and TEM photographs of the catalyst according toExample 1 after performing a dry CO₂ reforming reaction using thecatalyst for 200 hours.

FIGS. 9A-9B show SEM and TEM photographs of the catalyst according toComparative Example 1 after performing a dry CO₂ reforming reactionusing the catalyst prepared by the conventional wet method for 200hours.

FIGS. 10A-10B show three-dimensional SEM and TEM photographs of thecatalyst shown in FIGS. 9A-9B.

FIG. 11 is a SEM photograph of the catalyst according to Example 1 afterperforming a wet CO₂ reforming reaction using the catalyst at 850° C.for 200 hours.

FIGS. 12A-12B show SEM and TEM photographs of the catalyst according toComparative Example 1 after performing a wet CO₂ reforming reactionusing the catalyst at 850° C. for 200 hours.

FIGS. 13A-13B are graphs showing the results of measuring components ofa particle portion and other portions in the catalyst shown in FIGS.12A-12B by EDAX.

FIG. 14 is a graph showing the results of measuring thermogravimetricanalysis (TGA) and derivative thermogravimetry (DTG) of catalystsaccording to Example 1 and Comparative Example 1 after performing a wetCO₂ reforming reaction using the catalysts at 850° C. for 200 hours.

FIG. 15 is a graph showing the CH₄ conversion rate change and the H₂/COproduction ratio change of catalysts according to Example 1 andComparative Example 1 over time while performing a wet CO₂ reformingreaction using the catalysts at 850° C. for 200 hours.

FIG. 16 is a graph showing the volume change of catalysts according toExample 1 and Comparative Example 1 depending upon the increase ofpressure after the catalyst reaction at 850° C. for 200 hours.

FIG. 17 shows an NMR spectrum of catalysts according to Example 1 andComparative Example 1 before and after the reaction according toExperimental Example 3.

FIGS. 18A-18B are TEM photographs showing Ni particle shapes in eachcatalyst and graphene produced around the Ni particle after performing awet CO₂ reforming reaction using a catalyst according to Example 1 andthe catalyst according to Comparative Example 1 at 850° C. for 200hours.

DETAILED DESCRIPTION

It will be understood that when an element or layer is referred to asbeing “on,” “connected to,” “coupled to,” or “covering” another elementor layer, it may be directly on, connected to, coupled to, or coveringthe other element or layer or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly connected to,” or “directly coupled to” another elementor layer, there are no intervening elements or layers present. Likenumbers refer to like elements throughout the specification. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items.

It will be understood that, although the terms first, second, third,etc. may be used herein to describe various elements, components,regions, layers, and/or sections, these elements, components, regions,layers, and/or sections should not be limited by these terms. Theseterms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer, orsection. Thus, a first element, component, region, layer, or sectiondiscussed below could be termed a second element, component, region,layer, or section without departing from the teachings of exampleembodiments.

Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” may encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The terminology used herein is for the purpose of describing variousembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms,“comprises,” “comprising,” “includes,” and/or “including,” if usedherein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments should not be construed aslimited to the shapes of regions illustrated herein but are to includedeviations in shapes that result, for example, from manufacturing.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. It will be further understood that terms,including those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

According to one example embodiment, a CO₂ reforming catalyst is formedby supporting at least one catalyst metal in a porous carrier. Thecatalyst metal may be in the form of a particle that includes atransition metal. For instance, the transition metal maybe a Group 6-12element. The Group 6-12 element may be selected from the groupconsisting of Ni, Co, Cr, Mn, Mo, Ag, Cu, Zn, and Pd, although exampleembodiments are not limited thereto. The catalyst metal particle mayhave a half circular-shaped or half oval-shaped cross-sectional surfacewhen linearly cut in a vertical direction to the binding surface of thecatalyst metal particle and the porous carrier, although it should beunderstood that variations in shape are possible. Each catalyst metalparticle is chemically bound to the porous carrier (e.g., in a form ofan alloy). In addition, the porous carrier includes a protruding portionthat extends in a rod, needle, or sheet shape around the catalyst metalparticle. The extended protruding portions of the porous carrier and thecatalyst metal particle form a strong interaction with each other.

The catalyst metal particles may have an average size ranging from about1 nm to about 50 nm. The pores of the porous carrier may have an averagesize of about 1 μm or more. In a non-limiting embodiment a ratio of theaverage pore size to the average particle size may range from about 20to about 1000.

According to another example embodiment, the CO₂ reforming catalyst maybe prepared by the following method of preparing a CO₂ reformingcatalyst. The prepared catalyst may considerably reduce or prevent thedecrease of an active part of the catalyst caused by sintering acatalyst metal at a relatively high temperature and the degradation of acatalyst caused by carbon deposition (which are problems in theconventional CO₂ reforming catalyst).

The CO₂ reforming catalyst may be used as a catalyst for a CO₂ reformingreaction. The CO₂ reforming reaction may be expressed by generating H₂and CO from a dry catalyst reaction of CO₂ and CH₄ at a relatively hightemperature, and the reaction mechanism is a strong endothermic reactionas represented in following Reaction Scheme 1 and Reaction Scheme 2.Accordingly, the reaction may be performed at a temperature of greaterthan or equal to 650° C., but it may be beneficial to keep thetemperature to less than or equal to 850° C. for efficiency reasons.When using the catalyst according to one example embodiment, theactivity is enhanced at a temperature of 700 to 850° C. compared to theconventional catalyst, so as to expect a catalyst having higherefficiency.CH₄+CO₂→2CO+2H₂ΔHo=247.3kJ/mol  [Reaction Scheme 1]CO₂+H₂→CO+2H₂O ΔHo=41kJ/mol  [Reaction Scheme 2]

The problems in the reaction are the methane decomposition reaction (CH₄cracking) represented by the following Reaction Scheme 3 and thecatalyst performance degradation by catalyst coking which is generatedby depositing carbon on the catalyst surface according to the Boudouardreaction represented by the following Reaction Scheme 4, as well as theabove reaction. The methane decomposition reaction (CH₄ cracking)represented by the following Reaction Scheme 3 becomes the main causefor deactivating the catalyst, and the Boudouard reaction represented bythe following Reaction Scheme 4 is relatively less serious at a hightemperature.CH₄

C+2H₂ΔHo=122.3kJ/mol  [Reaction Scheme 3]2CO

C+CO₂ΔHo=125.2kJ/mol  [Reaction Scheme 4]

Carbon produced from the reaction deactivates the catalyst by decreasingthe reaction surface area of the catalyst, blocking pores, andaccelerating the decomposition of the supporter.

In addition, the sintering phenomenon of decreasing the active portionsof the catalyst during a relatively high temperature catalyst reactionis also a serious factor for degrading a catalyst. The sinteringindicates the phenomenon in which catalysts are coagulated with eachother and grown into larger particles due to the lack of thermalstability when the chemical reaction using a catalyst is carried out ata relatively high temperature. The pores of the carrier are decreased bythe sintering phenomenon, and the interface area of the catalyst/carrieris also decreased. Since the catalyst reaction is considered to beperformed at the interface between the catalyst and carrier, the activesurface area of catalyst is decreased and the reaction gas is hardlydiffused into the active portions of the catalyst when the interfacearea of the catalyst/carrier is decreased, and thus the binding force ofcatalyst/carrier is also decreased by narrowing the interface betweenthe carrier and catalyst. As the result of this phenomenon, theconversion rate of reaction gas is decreased in the reaction, theinternal pressure of the reactor is increased, and the durability of thecatalyst and carrier is deteriorated.

The CO₂ reforming catalyst according to one example embodiment isstabilized even at a relatively high temperature by the stronginteraction bond of the catalyst-carrier, and thus the size of thecatalyst metal particle is less changed even after participating in aCO₂ reforming reaction at a relatively high temperature to remarkablydecrease the coking due to Reaction Scheme 3 and Reaction Scheme 4.Accordingly, the carbon amount deposited on the surface of the catalystparticle is remarkably decreased, or the produced carbon is easilyremoved, and thus the life-span and durability of the catalyst areimproved.

In addition, the CO₂ reforming catalyst ensures thermal stability, sothe sintering phenomenon of decreasing active portions of the catalystis remarkably decreased during a relatively high temperature catalystreaction.

Studies using an inexpensive catalyst of Ni have been conducted for thehigh temperature dry catalyst reaction of CO₂ and CH₄. A Ni catalyst hasa benefit of price competitiveness compared to a noble metal catalyst,and also dissociates CO₂ and CH₄ at a relatively low temperature due toits relatively strong absorption with carbon. Therefore, a Ni catalystis mainly used in the reaction.

Since Ni causes degradation due to coking when having a catalystparticle size of greater than or equal to about 5 nm, the coking isprogressed by sintering the catalyst particle at a high temperaturereaction when the catalyst is used at the optimal catalyst supportedamount (about 5 to 8 wt %). Accordingly, when the prepared catalyst isthermally stabilized, the coking is reduced to provide a further stablecatalyst.

When the CO₂ reforming catalyst is prepared by supporting a catalystmetal such as Ni or the like in a porous carrier according to theconventional method of a wet process, immersing, co-precipitation,electro-plating, thermal evaporation, e-beam evaporation, or sputtering,the catalyst metal particle in the prepared catalyst forms an amorphoussphere, and the particles are physically bound to the surface of theporous carrier. In this case, the interaction between the catalyst metalparticle and the porous carrier is very weak. In addition, the catalysthas a smaller catalyst/carrier interface area between the catalyst andporous carrier.

FIG. 2 shows a cross-sectional view exaggerating the binding shape ofthe catalyst metal particle to the porous carrier in the conventionalCO₂ reforming catalyst. As shown in FIG. 2, in the conventionalcatalyst, catalyst metal particles are formed in a spherical shape andare weakly bound with the surface of an alumina carrier.

On the other hand, according to the CO₂ reforming catalyst of oneexample embodiment, the catalyst metal particle is chemically bound withthe porous carrier (e.g., in a form of an alloy) on the porous carrier.What is meant by the catalyst metal particle being bound with the porouscarrier in a form of an alloy is that each catalyst metal particle formsan atomic bond with the porous carrier. Assuming a nickel catalyst metalparticle and an alumina porous carrier, the atomic bonds may includeNi—Al and Ni—O—Al bonds. As a result, the catalyst metal particle willhave a half circular or half oval cross-sectional surface when linearlycut in the direction perpendicular to the binding surface with theporous carrier. The catalyst metal particle is attached to the porouscarrier by the strong interaction between the catalyst metal particleand the porous carrier as exaggeratingly shown in FIG. 1. In anon-limiting embodiment, the catalyst metal may cover about 10% to about100% of the surface of the porous carrier. For instance, at 100%, itshould be understood that the catalyst metal covers the entire surfaceof the porous carrier.

As shown in FIG. 1, when each catalyst metal particle is bound to thesurface of the porous carrier in a form of an alloy, thecarrier/catalyst interface is further widened compared to theconventional catalyst shown in FIG. 2. The binding force of thecarrier/catalyst is enhanced by increasing the interface area of thecarrier/catalyst. For example, about 10% to about 50% of the surfacearea of the catalyst metal particle may interface with the porouscarrier. In a non-limiting embodiment, about 10% to about 33% of thesurface area of the catalyst metal particle may interface with theporous carrier. Where the catalyst metal particle is a hemisphericalstructure, about 33% of the surface area of the catalyst metal particlemay interface with the porous carrier (πr²/[2πr²+πr²]). As a result ofthe increased interfacial binding area, the prepared catalyst is morestable at a relatively high temperature so as to reduce or prevent thesintering of the catalyst metal particle.

In addition, when widening the interface area of the carrier/catalyst,the efficiency of the CO₂ reforming reaction is further increased on theinterface thereof. FIG. 3 schematically shows the mechanism. As shown inFIG. 3, the CO₂ reforming catalyst according to one example embodimentmay more effectively perform the CO₂ reforming reaction through thewidened carrier/catalyst interface and may also further reduce thecoking and degradation phenomenon of the catalyst caused by depositingcarbon on the surface of the catalyst particle (which is a sidereaction). As shown in the left side of FIG. 3, in the conventionalNi-alumina catalyst, Ni particles are formed in a spherical shape, sothe interface area between the catalyst/carrier is significantly lowerthan the interface area between the catalyst/carrier according to oneexample embodiment shown in the right side of FIG. 3. As a result, theefficiency of the CO₂ reforming reaction for the conventional catalystis also lower and the carbon deposition phenomenon due to theside-reaction is also higher, which causes further deterioration.

In the catalyst according to an example embodiment, when a porouscarrier includes, for example, an alumina carrier, the carrier includesa protruding portion extended in a rod, needle, or sheet shape aroundthe catalyst metal particle. This is shown in FIG. 4. FIG. 4 shows SEM(scanning electron microscope) and TEM (transmission electronmicroscope) photographs of the CO₂ reforming catalyst according to oneexample embodiment including a catalyst metal of Ni and a porous carrierof alumina. FIG. 4A shows rod protruding portions formed by alumina. Therod-shaped protruding portion is formed by surrounding the catalystmetal particle bound with the alumina carrier, which is shown in detailin FIG. 4B. FIG. 4B shows hexagonal particles among rod-shaped carrierprotruding portions, which are Ni catalyst particles. FIG. 5A and FIG.5B are SEM (FIG. 5A) and TEM (FIG. 5B) photographs enlarging a part ofthe catalyst shown in FIG. 4 by differing the magnification. FIGS. 5Aand 5B may show the further detailed shapes and binding relationship ofthe catalyst metal particle and the porous carrier of the CO₂ reformingcatalyst according to one example embodiment.

FIG. 6 is a graph showing the components of a particle portion (FIG. 6A)and the other portions (FIG. 6B) in a Ni-alumina catalyst according toone example embodiment measured by an EDAX (Energy Dispersive x-raySpectroscopy) element analyzer.

FIG. 6A shows the results of measuring components of a portion expressedin a hexagon particle in the catalyst shown in FIG. 4 or FIG. 5. It isunderstood that the hexagon particle is a Ni metal particle since Ni ismostly included. FIG. 6B shows the results of measuring the rod-shapedprotruding portion in the catalyst, and it is understood that aluminum(Al) is most detected, so the protruding portion is derived from thecarrier. In other words, it is understood that the hexagon particlesexpressed in TEM photographs or the like of FIG. 4 and FIG. 5 are Nicatalyst particles, and the rod-shaped protruding portions are derivedfrom the carrier.

As shown in the SEM photograph and TEM photograph for the surface of theNi-alumina catalyst prepared by the conventional general method in FIG.7, it is understood that the catalyst does not include extendingrod-shaped protruding portions of alumina, differing from one exampleembodiment of the present disclosure.

In the CO₂ reforming catalyst according to one example embodiment, thecatalyst metal particle is bound with the surface of the carrier in aform of an alloy, and simultaneously, the carrier forms a rod, needle,or sheet-shaped protruding portion around the catalyst metal particle,so a relatively strong interaction between the catalyst metal particleand the carrier is provided. Therefore, the bond between thecatalyst-carrier is further stabilized to reduce or prevent thesintering between the catalyst metal particles and to decrease thecarbon deposition on the surface of the catalyst particle even afterbeing used in the CO₂ reforming reaction represented by Reaction Scheme5 at a relatively high temperature for a long time, for example, atabout 700 to about 900° C. for about 10 hours to about 200 hours, andspecifically, at about 700 to about 850° C. for about 10 hours to about200 hours. Accordingly, the size of the catalyst particle after beingused in the CO₂ reforming reaction has a growth rate of only about 5 toabout 10% relative to the size of the catalyst particle before beingused in the reaction. In other words, the catalyst may reduce or preventthe catalyst degradation and maintain the catalyst activity even whenbeing used at a relatively high temperature for a relatively long time,so the life-span of the catalyst may be significantly prolonged.

The CO₂ reforming catalyst according to one example embodiment may havea relatively uniform diameter average of the catalyst metal particlesbefore being used in the CO₂ reforming reaction within the range ofabout 2 to about 20 nm, specifically, about 10 to about 20 nm, asunderstood from FIG. 4 and FIG. 5. The growth rate of the catalystparticle before and after the reaction is also within a range of about 5to about 10%. The size of the catalyst metal particle is insignificantlychanged even after the catalyst reaction at a relatively hightemperature (850° C.). Considering that the catalyst particle is moresintered at a relatively high temperature reaction when having thegreater diameter of the catalyst particle, the catalyst particle size ofthe catalyst according to one example embodiment may be effective inreducing or preventing the sintering and maintaining the catalyst activespecific surface area to improve the activity of the catalyst.

In addition, it is understood that in the catalyst according to oneexample embodiment, the average length of the rod-shaped protrudingportion of the porous carrier is maintained between about 10 and about20 nm as shown in FIG. 4 and FIG. 5.

FIG. 8 shows SEM (FIG. 8A) and TEM (FIG. 8B) photographs of the CO₂reforming catalyst according to Example 1 after performing a dry CO₂reforming reaction using the catalyst for 200 hours. From thephotographs, it is understood that the catalyst particle size isinsignificantly increased before and after the catalyst reaction sincethe size of the catalyst metal particle is maintained between about 20and about 30 nm even after participating in the reaction at a relativelyhigh temperature for 200 hours. In addition, it is understood that theshape, the binding structure, or the like of the catalyst metal particleand the protruding portion derived from rod-shaped alumina in thecatalyst are not changed, and the relatively strong bond between them ismaintained as it was.

On the other hand, in the case of Ni—Al catalyst prepared according tothe conventional wet process (Comparative Example 1), as shown in FIG.9, it is understood that whisker-type carbon nanotubes are produced inthe catalyst by the carbon deposition after being used in the dry CO₂reforming reaction at a relatively high temperature for 200 hours (FIG.9A). In addition, as shown in FIG. 9B, it is understood that thecatalyst particle has a non-uniform size from about 20 nm to about 100nm, and also has an amorphous shape.

FIG. 10 shows three-dimensional SEM and TEM images of the Ni—Al catalystprepared by a conventional wet process (Comparative Example 1), and itis understood that carbon nanotubes are formed between the catalystparticles in the catalyst by the carbon deposition after the hightemperature dry reaction, as shown in more detail in FIG. 10A. Inaddition, the catalyst particles are also formed in a relatively largebundle by sintering with each other during the reaction at a relativelyhigh temperature.

On the other hand, the CO₂ reforming catalyst according to one exampleembodiment may also be used for the wet reforming reaction of CO₂represented by the following Reaction Scheme 5.3CH₄+CO₂+2H₂O→4CO+8H₂  [Reaction Scheme 5]

The CO₂ reforming reaction performs a reaction by adding water as wellas CH₄ and CO₂, which are the reactants of the reaction for reformingCO₂ as understood from the Reaction Scheme. As a result, H₂ and CO maybe obtained as final products in the molar ratio of H₂/CO of 2.

FIG. 11 shows SEM and TEM image photographs of the NiAl catalystaccording to one example embodiment (Example 1) after being used in theCO₂ wet reforming reaction at 850° C. for 200 hours. From the drawing,it is understood that, in the catalyst according to Example 1, the Niparticle maintains the hexagonal shape having a size of about 20 nm evenafter performing the wet reforming reaction at a relatively hightemperature for about 200 hours, and the rod-shaped alumina carrier isstill present around the Ni particle. In other words, it is understoodthat a relatively stable bond between the catalyst particle and thecarrier is maintained by the relatively high interaction thereof, and ismaintained even in the wet reforming reaction at a relatively hightemperature.

On the other hand, in the catalyst according to Comparative Example 1prepared by the conventional method, the Ni particle has an amorphousirregular shape and a non-uniform particle size of about 20-100 nm asshown in FIG. 12A. In addition, it is found that coarse carbon nanotubesare formed among the Ni particles.

FIG. 13 shows the components of each portion of the catalyst shown inFIG. 12 measured by EDAX. FIG. 13A shows the results of measuring theportion expressed in the circular particle in FIG. 12, and it isunderstood that the amorphous irregular particles shown in FIG. 12 areNi catalyst particles since Ni is mostly detected in the portion. Inaddition, FIG. 13B shows the results of measuring the portions otherthan the circular particle in FIG. 12, and it is understood that thecatalyst is deposited with carbon during the wet reforming reaction at arelatively high temperature since it includes a relatively high amountof carbon.

FIG. 14 is a graph showing the results of thermogravimetric analysis(TGA) and derivative thermogravimetric analysis (DTG) of catalystsaccording to Example 1 and Comparative Example 1 after performing a wetCO₂ reforming reaction at a relatively high temperature for 200 hours.From FIG. 14, it is understood that weight is lost in ComparativeExample 1 which means that coking has occurred in the catalyst accordingto Comparative Example 1. On the other hand, weight is lost to a lesserextent in the catalyst according to Example 1, which means that cokingis occurring at a lesser extent in the catalyst. The results calculatedfrom the graph show that the carbon deposition amount of the catalystaccording to Example 1 is relatively low, at a level of about 40%relative to the catalyst according to Comparative Example 1.

In the CO₂ reforming catalyst according to one example embodiment, thecatalyst metal may be at least one selected from the group consisting ofNi, Co, Cr, Mn, Mo, Ag, Cu, Zn, and Pd. In a non-limiting embodiment,the catalyst metal particle may be a particle formed entirely of Ni. Inanother non-limiting embodiment, the catalyst metal particle may be aparticle that includes Ni and one or more of the above-mentioned metalsand/or other metal(s). The catalyst metal of Ni, Co, Cr, Mn, Mo, Ag, Cu,Zn, and Pd has a lower cost compared to a noble metal catalyst metal,and also has a relatively high temperature stability or the like, so itis useful as a CO₂ reforming reaction catalyst at a relatively hightemperature.

According to one example embodiment, in the CO₂ reforming catalyst usingNi as a catalyst metal, the Ni metal may form a particle having ahexagonal surface in the state of being supported in the porous carrier.In other words, differing from the catalyst prepared by the conventionalmethod, the CO₂ reforming catalyst according to one example embodimenthas a half circular or half oval cross-sectional surface when linearlycut in a direction perpendicular to the binding surface between thecatalyst metal particle and the porous carrier, and also each catalystmetal particle may have a hexagonal surface.

The porous carrier may be an oxide. For example, the oxide may be atleast one selected from the group consisting of alumina, titania, ceria,and silica oxide.

In the CO₂ reforming catalyst, when the carrier is, for example,alumina, silica, or the like, the carrier may maintain the stable γshape even after participating in a relatively high temperature catalystreaction due to the relatively rigid carrier characteristic, so as toimprove the durability and life-span characteristics of the catalyst.

In the CO₂ reforming catalyst, a porous carrier having a larger specificsurface area is better. For example, the porous carrier may have aspecific surface area of about 20 to about 500 m²/g, and specificallyabout 100 to about 500 m²/g.

As described in the above, the CO₂ reforming catalyst according to oneexample embodiment suppresses the sintering between catalyst particleseven after the reforming reaction at a relatively high temperature, andreduces or prevents the carbon deposition to the catalyst particle andthe decrease of the size of the carrier pores. Thereby, the specificsurface area of the porous carrier is decreased after using the catalystin the CO₂ reforming reaction at 700 to 900° C., and specifically 700 to850° C., for 10 to 200 hours by only about 5% to about 30% compared tobefore participating in the reforming reaction.

The CO₂ reforming catalyst may affect the degree of activity accordingto the supported concentration of the catalyst metal. For example, inthe CO₂ reforming catalyst, the supported concentration of the catalystmetal may range from about 1 to about 20 wt %, and specifically about 4to about 8 wt %.

In one example embodiment, when the CO₂ reforming catalyst is formed byusing Ni as a catalyst metal and alumina as a porous carrier in theabove weight ratio, the catalyst has Ni in a volume ratio of about 0.4to about 7.5%, for example, about 0.44% to about 7.32%, and alumina in avolume ratio of about 99.5% to about 92.5%, for example, about 99.56% toabout 92.68%, since Ni has a density of about 8.9 and alumina (Al₂O₃)has a density of about 4.

The CO₂ reforming catalyst decreases the degradation of the catalysteven after the dry and wet CO₂ reforming reaction at a relatively hightemperature for a relatively long time, so the activity of the catalystis maintained for a long time, and the catalyst life-span is extended.

FIG. 15 is a graph showing the CH₄ conversion rate and the producedH₂/CO ratio by lapse of time when the catalyst according to Example 1prepared by the method according to one example embodiment and thecatalyst according to Comparative Example 1 prepared by the conventionalmethod participate in the CO₂ wet reforming reaction at a relativelyhigh temperature (850° C.) for 200 hours. From the graph, it isunderstood that the CH₄ conversion rate is less decreased by the lapseof time in the case of using the catalyst according to Example 1, butthe CH₄ conversion rate is relatively more decreased by the lapse oftime in the case of using the catalyst according to ComparativeExample 1. In addition, the produced H₂/CO ratio relatively maintainsthe ratio of about 2 even by the lapse of time in the catalyst accordingto Example 1, but the ratio is increased to over 2 by the lapse of timein the catalyst according to Comparative Example 1. In other words, itis understood that the relatively high temperature wet CO₂ reformingreaction for reaching the H₂/CO ratio to about 2 is badly maintained inthe case of using the catalyst according to Comparative Example 1. Fromthe results, it is understood that in the catalyst according to oneexample embodiment, the catalyst activity is maintained even during thereaction at a relatively high temperature for a relatively long time,the life-span of the catalyst is extended, and the durability to thedegradation is provided.

On the other hand, the wet catalyst method of reforming CO₂ using theCO₂ reforming catalyst may provide graphene on the surface of thecatalyst metal particle of the CO₂ reforming catalyst as a side-product,as well as CO and H₂ which are products of reforming CO₂ represented byReaction Scheme 5. The graphene may be formed in 1-5 layers on thesurface of the catalyst metal particle during the reaction. The reactionof producing graphene from the reactants CH₄ and CO₂ may be representedby the following Reaction Scheme 6 and Reaction Scheme 7.CH₄

2H₂+C  [Reaction Scheme 6]2CO

CO₂+C  [Reaction Scheme 7]

FIG. 18A is a TEM photograph showing that a thin graphene layer isformed around the Ni particle of the catalyst prepared according toExample 1, after applying the wet reforming reaction. On the other hand,multi-layered graphite is formed around the Ni particle of the catalystaccording to Comparative Example 1 when applying the same reaction.

Studies on preparing graphene are actively progressing since the variousstructural and chemical properties thereof are desirable, but it is noteasy to provide graphene at a relatively low price and with a relativelylarge area. However, the wet catalyst reaction using the CO₂ reformingcatalyst according to one example embodiment may produce graphene havingan industrially-useful application at a relatively low price. On theother hand, the conventional catalyst produces only whisker-type carbonnanotubes as a side-reactant which causes the catalyst degradation bythe carbon deposition. In addition, the method of preparing graphene isa reaction simply using a catalyst, which has merits of very simpleprocess conditions compared to the many well known methods of preparinggraphene.

According to another example embodiment, a method of preparing the CO₂reforming catalyst is provided. The method includes the following steps:

immersing a porous carrier into a precursor solution of at least onecatalyst metal (e.g., selected from the group consisting of Ni, Co, Cr,Mn, Mo, Ag, Cu, Zn, and Pd) and drying the same to provide acatalyst-carrier complex in which the particles of the catalyst metalare supported in the porous carrier;

firing the catalyst-carrier complex at a temperature of less than orequal to 900° C. under the presence of nitrogen (N₂) or hydrogen (H₂)gas;

purging the fired catalyst-carrier complex with the inert gas andreducing the same;

immersing the reduced catalyst-carrier complex in water; and

reducing the water-immersed catalyst-carrier complex with water andhydrogen.

The CO₂ reforming catalyst prepared according to the method has a halfcircular or half oval-shaped cross-sectional surface when linearlycutting in a direction perpendicular to the binding surface of thecatalyst metal particle and the porous carrier by binding each catalystmetal particle to the porous carrier in a form of an alloy. The porouscarrier includes a protruding portion extended in a rod, needle, orsheet shape around the catalyst metal particle.

In the method, the catalyst-carrier complex may be fired at atemperature of less than or equal to 900° C., specifically, atemperature of about 450 to about 900° C., and more specifically, atemperature of about 500 to about 850° C.

In the method, the purging of the fired catalyst-carrier complex withinert gas may be performed by purging with nitrogen (N₂), helium (He),or argon (Ar) gas for about 5 to about 20 minutes, specifically, forabout 10 minutes.

In the method, the reducing the catalyst-carrier complex after thepurging of the catalyst-carrier complex with inert gas includes heatingthe same under the hydrogen gas atmosphere at about 500 to about 900° C.for about 1 hour, specifically, at about 850° C. for about 1 hour.

In the method, the immersing the reduced catalyst-carrier complex inwater may include adding water to the reduced catalyst-carrier complex.Particularly, the reduced catalyst-carrier complex may be cooled beforeadding water thereto.

The reducing the water-immersed catalyst-carrier complex with water andhydrogen includes supplying water and hydrogen gas to thecatalyst-carrier complex while heating from room temperature until about800° C. to about 900° C., specifically, until about 850° C.

Hereinafter, various embodiments are illustrated in more detail withreference to several examples. However, the following are merely exampleembodiments and are not intended to be limiting.

EXAMPLES Example 1

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared according to an early wetprocess. Alumina (150 m²/g, alumina granule diameter: −3 mm φ, Alfa) isimmersed in a Ni(NO₃)₂H₂O (Samchun) aqueous solution and dried in anoven at 120° C. for 24 hours and fired at 900° C. under a nitrogen (N₂)gas atmosphere for 1 hour. The fired catalyst is purged with He gas at500° C. for 10 minutes and then maintained at 850° C. under the hydrogenatmosphere for 1 hour to provide 7 wt % of a Ni/γ-Al₂O₃ catalyst. Areactor is cooled at 30° C., and 5 ml of distilled water is added to thecatalyst. Then the water is evaporated by heating (10° C./minute) undera hydrogen atmosphere and maintained at 850° C. for one hour.

The SEM and TEM images of the prepared catalyst are taken to show theshape of the catalyst metal particle and the shape of the carrier(referring to FIG. 4). The catalysts are examined using theultra-high-resolution field emission scanning electron microscopy(UHR-FE-SEM; Hitachi S-5500, resolution 0.4 nm) with transmissionelectron microscopy (TEM) operating at 30 kV. Elemental composition isassessed using an energy dispersive X-ray spectroscopy (EDS) inconjunction with the UHR-FE-SEM. The specimens for EM characterizationwere prepared by spreading a droplet of ethanol suspension containingthe sample onto a copper grid coated with a thin layer of amorphouscarbon film and allowing it to dry in air.

FIG. 4A is the SEM image showing that the alumina carrier is formed witha protruding portion extended in a rod shape. FIG. 4B is the TEM imageshowing that the rod-shaped protruding portion of alumina is formedaround the hexagonal Ni catalyst particle, so the catalyst metalparticle and the alumina carrier are bound by a relatively stronginteraction.

FIG. 5 shows SEM (FIG. 5A) and TEM (FIG. 5B) photographs taken fromparts of FIG. 4A and FIG. 4B with differing magnification, so that theshapes of the hexagonal Ni catalyst particle and the rod-shaped aluminaare further shown in detail.

Example 2

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared in accordance with the sameprocedure as in Example 1, except that alumina (150 m²/g, aluminagranule diameter: −3 mm φ, Alfa) is immersed in a Ni(NO₃)₂H₂O (Samchun)aqueous solution and dried in an oven at 120° C. for 24 hours and thenfired at 900° C. under the hydrogen (H₂) gas atmosphere for 1 hourinstead of firing at 900° C. under the nitrogen (N₂) gas atmosphere.

Comparative Example 1

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared according to the early wetprocess. Alumina (150 m²/g, alumina granule diameter: −3 mm φ, Alfa) isimmersed in a Ni(NO₃)₂H₂O (Samchun) aqueous solution and dried in anoven at 120° C. for 24 hours and fired at 500° C. under the airatmosphere for 5 hours. The fired catalyst is reduced under the nitrogenatmosphere while heating (10° C./minute) and maintained at 850° C. underthe hydrogen atmosphere for one hour to provide a 7 wt % of Ni/γ-Al₂O₃catalyst.

The prepared catalyst is photographed to provide SEM and TEM images(referring to FIG. 7) as in Example 1. FIG. 7A is the SEM image whichdoes not show a rod-shaped bundle of the alumina carrier, differing fromFIG. 4A. The TEM image shown in FIG. 7B also does not show therod-shaped protruding portion of alumina carrier, and the shape of theNi catalyst particle is amorphous rather than hexagonal as shown in FIG.4B.

Comparative Example 2

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared in accordance with the sameprocedure as in Example 1, except that alumina (150 m²/g, aluminagranule diameter: −3 mm φ, Alfa) is immersed in a Ni(NO₃)₂H₂O (Samchun)aqueous solution and dried in an oven at 120° C. for 24 hours and thenfired at 500° C. under the air atmosphere for 1 hour instead of firingat 900° C. for 1 hour under the nitrogen (N₂) gas atmosphere.

Comparative Example 3

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared in accordance with the sameprocedure as in Example 1, except that alumina (150 m²/g, aluminagranule diameter: −3 mm φ, Alfa) is immersed in a Ni(NO₃)₂H₂O (Samchun)aqueous solution and dried in an oven at 120° C. for 24 hours and thenfired at 900° C. under the air atmosphere for 1 hour instead of firingat 900° C. under the nitrogen (N₂) gas atmosphere.

Comparative Example 4

7 wt % of a Ni/γ-Al₂O₃ catalyst is prepared in accordance with the sameprocedure as in Example 1, except that alumina (150 m²/g, aluminagranule diameter: −3 mm φ, Alfa) is immersed in a Ni(NO₃)₂H₂O (Samchun)aqueous solution and dried in an oven at 120° C. for 24 hours and thenfired at 1000° C. under the air atmosphere for 1 hour instead of firingat 900° C. under the nitrogen (N₂) gas atmosphere.

Experimental Example 1

The catalyst prepared from Example 1 is analyzed for the componentsusing an EDAX (Energy Dispersive x-ray Spectroscopy) element analyzer.In other words, from the results of measuring the hexagonal particleportion and the rod portion of the catalyst, it is understood that thehexagonal particle portion corresponds to the Ni catalyst particle sinceit has a high amount of Ni (FIG. 6A), and the rod-shaped protrudingportion is derived from the alumina carrier since it has a high amountof Al (FIG. 6B). Thereby, the shape of the catalyst metal particle andthe alumina carrier may be confirmed in the catalyst obtained fromExample 1.

Experimental Example 2

Using the catalysts prepared from Example 1 and Comparative Example 1, adry reforming reaction of CO₂ and CH₄ is performed as in followingReaction Scheme 1 and Reaction Scheme 2. 0.45 g of each catalystprepared from Example 1 and Comparative Example 1 is added withreactants of CH₄ and CO₂, nitrogen is flowed in each at 200 sccm(standard cubic centimeter per minute) at 850° C., and the reaction iscarried out for 200 hours (gas hourly space velocity (GHSV)=56 kcc/g·hr).CH₄+CO₂→2CO+2H₂  [Reaction Scheme 1]CO₂+H₂→CO+2H₂O  [Reaction Scheme 2]

After the reaction, the catalysts according to Example 1 and ComparativeExample 1 are photographed to obtain SEM and TEM images.

From FIGS. 8A and 8B, the catalyst according to Example 1 maintains ahexagonal shape having a size of 20-30 nm even after the reformingreaction at a high temperature for 200 hours, and the rod-shaped aluminacarrier is still present around the Ni particle as shown in FIG. 8B, soit is understood that the stable bond between the catalyst particle andthe carrier is maintained by the high interaction between them.

On the other hand, in the catalyst according to Comparative Example 1shown in FIG. 9A, the Ni particle has an irregular shape and anon-uniform size of about 20-100 nm. In addition, the bold line betweenthe Ni particles is found, which is more clearly shown in FIG. 10showing three-dimensional SEM and TEM photographs. FIG. 10A is a 3D SEMphotograph showing that Ni particles are agglomerated with each otherand sintered, and that whisker-type long carbon nanotubes are formedbetween the particles. In other words, in the catalyst according toComparative Example 1, a coking phenomenon occurs by carbon depositionduring the reforming reaction at a high temperature.

Experimental Example 3

Using the catalysts according to Example 1, Example 2, ComparativeExample 1, and Comparative Example 2, a wet reforming reaction of CO₂and CH₄ is performed according to following Reaction Scheme 5. 0.45 g ofeach catalyst obtained from Example 1, Example 2, Comparative Example 1,and Comparative Example 2 is added with CH₄:CO₂:H₂O:N₂ in a molar ratioof 1:0.4:0.81:1.6 at 850° C. under 1 atm and reacted with the reactionrepresented by the following Reaction Scheme 5 for 200 hours (gas hourlyspace velocity (GHSV, CH₄ basis)=13,333 ml/g·h), entire gas 50,666ml/g·h basis).3CH₄+CO₂+2H₂O→4CO+8H₂  [Reaction Scheme 5]

The catalysts according to Example 1 and Comparative Example 1 arephotographed to provide SEM and TEM images after the reaction.

As shown in FIG. 11, in the catalyst according to Example 1, the Niparticle maintains the hexagonal shape having a size of about 20 nm evenafter the wet reforming reaction at a relatively high temperature for200 hours, and a rod-shaped alumina carrier is still present around theNi particle. In other words, the stable bond between the catalystparticle and the carrier is maintained by the high interaction and isalso maintained even after a high temperature wet reforming reaction.

On the other hand, in the catalyst according to Comparative Example 1,the Ni particle has an amorphous and irregular shape and a non-uniformparticle size of about 20-100 nm as shown in FIG. 12A. In addition,coarse carbon nanotubes are found between the Ni particles.

FIG. 13 shows the results of measuring components of each portion of thecatalyst according to Comparative Example 1 shown in FIG. 12 by EDAX. Asshown in FIG. 13A, it is understood that the particle shown in the roundshape in the photograph of FIG. 12 is a Ni catalyst particle, and fromFIG. 13B, it is understood that carbon is highly deposited on thecatalyst during the relatively high temperature wet reforming reaction.

FIG. 14 is a graph showing the results of measuring thermogravimetricanalysis (TGA) and derivative thermogravimetry (DTG) of catalystsaccording to Example 1 and Comparative Example 1 after performing a wetreforming reaction according to Experimental Example 3 for 200 hours. InComparative Example 1, the weight loss means that coking has occurred,but it is confirmed that coking rarely occurs since little weight islost in Example 1.

In addition, the deposition amount of carbon of the catalysts accordingto Example 1 and Comparative Example 1 after the relatively hightemperature wet reforming reaction for 200 hours is calculated from theTGA and DTG graphs, and the results are shown in the following Table 1.

TABLE 1 Deposition amount of carbon Reaction (mg C/g catalyst h) timeCatalyst of 0.45 200 hours Example 1 Catalyst of 0.87 200 hoursComparative Example 1

From Table 1 and the graph shown in FIG. 14, it is understood that whenthe CO₂ reforming reaction is performed using the catalyst according tothe examples, the deposition amount of carbon is remarkably decreasedcompared to the catalyst prepared by the conventional method.

FIG. 15 is a graph showing the CH₄ conversion rate and the H₂/CO ratioof catalysts by lapse of time while performing the reaction using thecatalysts according to Example 1 and Comparative Example 1 in accordancewith the procedure of Experimental Example 3. The graph shows that theCH₄ conversion rate is insignificantly decreased in the case of usingthe catalyst according to Example 1, but the CH₄ conversion rate isrelatively significantly decreased by lapse of time in the case of usingthe catalyst according to Comparative Example 1. In addition, the H₂/COratio is relatively well maintained at about 2 even through lapsing oftime in the case of using the catalyst according to Example 1, but theratio is increased to over 2 in the case of using the catalyst accordingto Comparative Example 1. In other words, the high temperature wet CO₂reforming reaction is not maintained enough to maintain the H₂/CO ratioat 2 in the case of using the catalyst according to ComparativeExample 1. Thereby, it is understood that the catalyst according toExample 1 maintains the catalyst activity at a high temperature for along reaction time, so as to extend the catalyst life-span and toprovide durability against catalyst degradation.

The catalysts prepared from Example 1, Example 2, Comparative Example 1,and Comparative Example 2 undergo the procedure according toExperimental Example 3, and then each catalyst is measured for the CH₄and CO₂ conversion rate, the deposition rate of carbon to the catalyst,the Ni particle size change, and the growth rate of Ni particles after200 hours. The results are shown in following Table 2.

TABLE 2 Size Growth Conversion Reaction time Deposition changes of rateof Ni rate (h) rate of carbon Ni particle particle Catalyst (%) 1 200(mgC/gcat · h) (nm) (%) Example 1 CH₄ 98.5 97.9 0.082 10.5 → 12   14 CO₂82.6 82.2 Example 2 CH₄ 98.3 97.5 0.18 13 → 15 15 CO₂ 82.4 82.0Comparative CH₄ 98.3 97.1 0.45 17 → 20 17 Example 2 CO₂ 82.4 81.2Comparative CH₄ 94 90.8 0.87  7 → 22 214  Example 1

As shown in Table 2, in the catalysts of Example 1 and Example 2, theCH₄ and CO₂ conversion rates are very good, the deposition rate ofcarbon to the catalyst is very slow, the size changes of Ni particlesranges from about 12 nm and about 15 nm, respectively, which ismaintained in a very small size, and the growth rate of particles isonly about 14% and 15%, respectively, even after the reaction for 200hours.

On the other hand, in the catalyst according to Comparative Example 2using a firing gas of air instead of nitrogen or hydrogen gas, the CO₂conversion rate and the CH₄ conversion rate are relatively low, and thedeposition rate of carbon is somewhat high. In addition, after thereforming reaction at 850° C. for 200 hours, the Ni particle size is alittle larger than those of Example 1 and Example 2, and the growth rateof Ni particles is a little higher.

In addition, the catalyst according to Comparative Example 1 prepared bythe conventional initial wet process has the relatively lowest CO₂conversion rate and CH₄ conversion rate, and the highest deposition rateof carbon. In addition, after use in the reforming reaction at 850° C.for 200 hours, the Ni particle size is increased by even 214% comparedto before the reaction, so the Ni-alumina CO₂ reforming catalystprepared by the conventional method is significantly degraded by beingused in the CO₂ reforming reaction at a high temperature.

On the other hand, even though not shown in the data, the catalystaccording to Comparative Example 4 performing the firing reaction at atemperature (about 1000° C.) of greater than 900° C. has a very highcarbon deposition ratio, a larger size of Ni particles compared to othercomparative examples, and a very low CO₂ conversion rate and CH₄conversion rate.

Before and after the reaction according to Experimental Example 3, thecatalysts according to Example 1 and Comparative Example 1 are measuredfor the specific surface area (BET) and average pore diameter, and thechanges of BET and average pore diameter are shown in the followingTable 3.

The BET surface area and the pore volume of the catalysts were measuredby N₂ adsorption at −196° C. using a BET instrument (BELsorp, BEL,Japan). Approximately 0.1 g of catalyst was used for each analysis. Thedegassing temperature was 200° C. to remove the moisture and otheradsorbed gases from the catalyst surface.

TABLE 3 BET changes Changes of average pore Catalyst (m²/g) diameter(nm) Comparative 130.3 → 46.0 10.5 → 13.0 Example 1 Example 1  93.7 →68.6 19.3 → 22.6

From Table 3, it is understood that the catalyst according to Example 1has a smaller specific surface area (BET) compared to the catalystaccording to Comparative Example 1 due to the alloy binding shape of thecatalyst particle and the carrier, but the catalyst according to Example1 after the reaction at a high temperature for 200 hours less decreasesthe specific surface area compared to the catalyst according toComparative Example 1. In other words, even after the reaction at a hightemperature for 200 hours, the sintering and coking of the catalyst aresuppressed, so the catalyst may maintain the specific surface area to ahigher degree.

In addition, both catalysts according to Example 1 and ComparativeExample 1 increase the average pore diameter of the catalyst after thereaction, but the average pore diameter of the case of ComparativeExample 1 is more changed compared to that of Example 1. This is becausecarrier pores having a smaller diameter are clogged by the carbondeposition or the like during the reaction, and resultantly only largerpores remain in a carrier. Thereby, in the case of Comparative Example1, more carbon is deposited during the reaction compared to the case ofExample 1 to clog the small pores more to increase the average porediameter relative to the catalyst of Example 1.

FIG. 16 is a graph showing the relative volume change of catalystsaccording to Example 1 and Comparative Example 1 depending uponincreasing the relative pressure after the test according toExperimental Example 3. FIG. 16 also illustrates the results ofmeasuring the specific surface area (BET) of the catalyst shown in Table3. The catalyst according to Example 1 has a little change of thecatalyst BET and the average pore diameter of the carrier after thereaction, so the volume is less changed and is steadily maintainedaccording to the change of pressure. On the other hand, the catalystaccording to Comparative Example 1 remarkably decreases the BET ofcatalyst after high temperature reaction and further increases theaverage pore diameter of carrier, so it is understood that the volume ofthe catalyst is more significantly decreased according to an increase inthe pressure.

FIG. 17 shows an NMR (NMR (600 MHz) 2007, AVANCE III 600 Bruker)spectrum of catalysts according to Example 1 and Comparative Example 1before and after the reaction according to Experimental Example 3.

From the NMR spectrum, it is estimated that the catalyst according toExample 1 has less Lewis acid causing the carbon deposition since theNMR Td peak is high.

The ²⁷Al NMR peak region rate of Comparative Example 1 and Example 1before and after the reaction according to Experimental Example 3 isshown in the following Table 4.

TABLE 4 Catalyst ²⁷Al NMR peak region rate (Al_(Td)/Al_(Oh)) ComparativeBefore 0.37 Example 1 reaction After 0.27 reaction Example 1 Before 0.38reaction After 0.33 reaction

As illustrated in Table 4, it is confirmed that the catalyst accordingto Example 1 has a ²⁷Al NMR peak region rate (Al_(Td)/Al_(Oh)) ofgreater than or equal to 0.30 even after the reaction at a relativelyhigh temperature for a relatively long time, and it generally rangesfrom about 0.30 to about 0.45, even though not shown in the data.

FIG. 18 is a TEM image of the Ni particle after performing a CO₂reforming reaction of Experimental Example 3 using the catalystsaccording to Example 1 and Comparative Example 1. FIG. 18A shows the Niparticle in the catalyst according to Example 1. As shown in thedrawing, it is understood that the Ni particle has a hexagonal shape andis formed with a thin belt around the same which is a graphene layer. Inother words, the catalyst according to Example 1 forms 1-5 layeredgraphene as a side-reaction product on the surface of the catalystparticle during the CO₂ wet reforming reaction at a high temperature.FIG. 18B shows the results of measuring the catalyst according toComparative Example 1, and it is understood that the catalyst particleaccording to Comparative Example 1 has an amorphous shape, and amultilayered graphene layer is formed around the same. That is, it isconfirmed that 1-5 layered graphene is formed around the catalystparticle according to Example 1, while on the other hand, a carbon layerof nearly graphite rather than substantially graphene is formed aroundthe catalyst particle according to Comparative Example 1.

While example embodiments have been disclosed herein, it should beunderstood that other variations may be possible. Such variations arenot to be regarded as a departure from the spirit and scope of exampleembodiments of the present application, and all such modifications aswould be apparent to one skilled in the art after reviewing thedisclosure are intended to be included within the scope of the followingclaims.

What is claimed is:
 1. A CO₂ reforming catalyst comprising: a porouscarrier including a framework and protruding portions defining aplurality of pores therein; and at least one catalyst metal particlewithin the plurality of pores of the porous carrier, the at least onecatalyst metal particle including a transition metal, the at least onecatalyst metal particle being chemically bound to the porous carrier,the at least one catalyst metal particle having a deformed surface thatconforms to a receiving surface of the porous carrier.
 2. The CO₂reforming catalyst of claim 1, wherein the transition metal is selectedfrom a Group 6-12 element.
 3. The CO₂ reforming catalyst of claim 2,wherein the Group 6-12 element is at least one selected from the groupconsisting of Ni, Co, Cr, Mn, Mo, Ag, Cu, Zn, and Pd.
 4. The CO₂reforming catalyst of claim 1, wherein the porous carrier is an oxide.5. The CO₂ reforming catalyst of claim 4, wherein the oxide is at leastone selected from the group consisting of alumina, titania, ceria, andsilica.
 6. The CO₂ reforming catalyst of claim 1, wherein a majority ofthe at least one catalyst metal particle is Ni.
 7. The CO₂ reformingcatalyst of claim 6, wherein the Ni is present at a volume ratio ofabout 0.4% to about 7.5% based on a total volume of the CO₂ reformingcatalyst.
 8. The CO₂ reforming catalyst of claim 6, wherein the at leastone catalyst metal particle has a hexagonal shape.
 9. The CO₂ reformingcatalyst of claim 1, wherein the CO₂ reforming catalyst is configured tofacilitate a CO₂ reforming reaction represented by Reaction Scheme 5:3CH₄+CO₂+2H₂O→4CO+8H₂.  [Reaction Scheme 5]
 10. The CO₂ reformingcatalyst of claim 9, wherein the CO₂ reforming catalyst is configured tofacilitate the CO₂ reforming reaction at a temperature of about 700° C.to about 850° C.
 11. The CO₂ reforming catalyst of claim 10, wherein theat least one catalyst metal particle is configured to have a diametergrowth rate of about 5 to about 10% after about 10to 200 hours of theCO₂ reforming reaction.
 12. The CO₂ reforming catalyst of claim 10,wherein the at least one catalyst metal particle is configured such thata specific surface area of the porous carrier is decreased by about 5%to about 30% after about 10 hours to 200 hours of the CO₂ reformingreaction.
 13. The CO₂ reforming catalyst of claim 9, wherein the atleast one catalyst metal particle is configured such that graphene isproduced on the surface thereof as a side product of the CO₂ reformingreaction.
 14. The CO₂ reforming catalyst of claim 9, wherein the atleast one catalyst metal particle includes a plurality of catalyst metalparticles with an average longest diameter of about 2 nm to about 20 nmbefore the CO₂ reforming reaction.
 15. The CO₂ reforming catalyst ofclaim 9, wherein the porous carrier has a specific surface area of about20 m²/g to about 500 m²/g.
 16. The CO₂ reforming catalyst of claim 1,wherein the at least one catalyst metal particle has a halfcircular-shaped or half oval-shaped cross-sectional surface whenlinearly cut in a direction perpendicular to a binding surface of the atleast one catalyst metal particle and the porous carrier.
 17. The CO₂reforming catalyst of claim 1, wherein the protruding portions extend ina rod, needle, or sheet shape around the at least one catalyst metalparticle.
 18. The CO₂ reforming catalyst of claim 1, wherein theprotruding portions of the porous carrier has an average length of about5 nm to about 20 nm.
 19. The CO₂ reforming catalyst of claim 1, whereinthe at least one catalyst metal particle has a concentration of about 1wt % to about 15 wt % based on a total weight of the CO₂ reformingcatalyst.
 20. The CO₂ reforming catalyst of claim 1, wherein the porouscarrier is alumina and configured such that a ²⁷Al NMR peak region rate(Al_(Td)/Al_(Oh)) thereof ranges from about 0.30 to about 0.45 after acatalyst reaction at about 800° C. to about 900° C. for about 10 hoursto about 200 hours.